Add Canvas

Ooui/Canvas.cs

@@ -0,0 +1,36 @@
+using System;
+
+namespace Ooui
+{
+    public class Canvas : Element
+    {
+        Context2d context2d = new Context2d ();
+        int gotContext2d = 0;
+
+        public Canvas ()
+            : base ("canvas")
+        {
+        }
+
+        public Context2d GetContext2d ()
+        {
+            if (System.Threading.Interlocked.CompareExchange (ref gotContext2d, 1, 0) == 0) {
+                var mcall = Message.Call (Id, "getContext", "2d");
+                mcall.ResultId = context2d.Id;
+                Send (mcall);
+            }
+            return context2d;
+        }
+        protected override void SaveStateMessageIfNeeded (Message message)
+        {
+            switch (message.MessageType) {
+                case MessageType.Call when message.Key == "getContext" && message.Value is Array a && a.Length == 1 && "2d".Equals (a.GetValue (0)):
+                    AddStateMessage (message);
+                    break;
+                default:
+                    base.SaveStateMessageIfNeeded (message);
+                    break;
+            }
+        }
+    }
+}

Ooui/Client.js

@@ -75,7 +75,10 @@ function msgCall (m) {
     }
     const f = node[m.k];
     if (debug) console.log ("Call", node, f, m.v);
-    f.apply (node, m.v);
+    const r = f.apply (node, m.v);
+    if (typeof m.rid === 'string' || m.rid instanceof String) {
+        nodes[m.rid] = r;
+    }
 }
 
 function msgListen (m) {

Ooui/Context2d.cs

@@ -0,0 +1,10 @@
+namespace Ooui
+{
+    public class Context2d : EventTarget
+    {
+        public Context2d()
+            : base ("context2d")
+        {
+        }
+    }
+}

Ooui/Message.cs

@@ -19,6 +19,9 @@ namespace Ooui
         [JsonProperty("v", NullValueHandling = NullValueHandling.Ignore)]
         public object Value = null;
 
+        [JsonProperty("rid", NullValueHandling = NullValueHandling.Ignore)]
+        public string ResultId = null;
+
         public static Message Call (string targetId, string method, params object[] args) => new Message {
             MessageType = MessageType.Call,
             TargetId = targetId,

Tests/CanvasTests.cs

@@ -0,0 +1,23 @@
+using System;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+using Ooui;
+
+namespace Tests
+{
+    [TestClass]
+    public class CanvasTests
+    {
+        [TestMethod]
+        public void Context2dState ()
+        {
+            var c = new Canvas ();
+            Assert.AreEqual (1, c.StateMessages.Count);
+            var c2d = c.GetContext2d ();
+            Assert.AreEqual (2, c.StateMessages.Count);
+            var c2d2 = c.GetContext2d ();
+            Assert.AreEqual (2, c.StateMessages.Count);
+            Assert.AreEqual (c2d, c2d2);
+        }
+    }
+}